For people presented with the challenge
described by [1]},
a relation of identity between inputs and outputs
will be immediately apparent.
Moreover, they will also immediately grasp that
both inputs and outputs are made up of strings of digits
and that there is a correspondence between digit positions
in the input and digit positions in the output.
It is this intrinsic structure in the task
that makes it tractable for humans.
In contrast, the standard fully connected architecture
is indifferent to this structure,
and for such a network the task consists of identifying
one unexceptional one-to-one mapping from among many.
